1. Field of the Invention
The present invention is related to the field of fiber optics, and more particularly to the use of fiber optic delivery light guides and projection systems in surgical illumination systems including headlamps worn by a surgeon.
2. Prior Art
Surgical illumination systems provide a means for delivering visible light to the surgical working field. They are used both as stand-alone units that simply provide a fixed field of illumination and in conjunction with magnification systems such as surgical loupes. Ideally, the beam of light forming a field of illumination on a plane normal to the central axis of the light beam positioned at the surgical field should be coaxial with the surgeon's field of view. To achieve this condition, illumination systems may be either stationary or movable in position, and the size of the illuminated field may be either fixed or adjustable. Stationary illumination systems having a fixed illumination field are desirable when the field of view is fixed as with the use of surgical loupes having constant magnification. When the magnification of the illumination field is adjustable, then an adjustable beam diameter is required. If the illumination system is used as a stand-alone unit, variation in both the position and beam diameter is desirable to accommodate different surgical fields.
Illumination systems generally consist of three main components: (i) a delivery light guide, (ii) a light-projection system, and (iii) a mounting mechanism. In prior art systems, the light delivery cable forms a bundle of fiber optics coupled between a light source and the illumination system. The use of a fiber optic bundle as the delivery cable is required because of the constraints imposed by conventional illumination systems in the coupling of light from the source into a small target such as the collection endface of the cable. Use of a bundle of fibers having a relatively large combined diameter of typically 3-5 mm is required to enable an adequate amount of light to be coupled into the delivery cable so as to illuminate the surgical field with a sufficient amount of light.
The light-projection system of prior art illumination systems can be grouped into two general categories: those that involve a direct coupling between the output end of the delivery cable and a lens, and those that involve a compound coupling where a turning mirror and/or lens is disposed between the output end of the fiber and the lens to direct the light to the lens. In a headlamp having compound coupling projection system, such as the one disclosed in Kloots U.S. Pat. No. 4,516,190, adjustment of the beam diameter, and hence the resulting field of illumination, is controlled by means of an adjustable aperture such as an iris placed in the path of the light beam. In order to reduce the size of the illuminated field, the diameter of the iris' aperture must be proportionately reduced, which in turn also attenuates the light output from the system proportionate to the size of the illuminated field.
The mounting system of a headlamp is typically a headband to which is attached a variety of clamps, brackets, hinges, pivot mechanisms and the like for mounting and positioning of the projection system. For example, in one prior art headlamp (Chester U.S. Pat. No. 3,830,230), the light projection system is connected to a headband via two rotation joints coupled together by a pivot member that permits planar rotation of the headlamp about the headband.
Although surgical illumination systems have been in use for many years, each of the three components of prior art designs have a number of disadvantages. One disadvantage of the fiber optic bundle delivery light guide is its weight, which causes fatigue to the neck of the surgeon during use of the headlamp. In some designs, an attempt has been made to reduce the drag of the bundle by bifurcating it so as to provide greater balance of the mounting assembly on the surgeon's head. Another disadvantage of fiber optic bundles is that the length of the delivery cable is rather limited because the loss of light per unit length is quite high, ranging from 10 to 15% per foot. The longer the cable, the less light available to the surgeon, thereby requiring shorter lengths of cable for larger diameter bundles. In practice, a delivery cable made from a fiber optic bundle having a diameter of 5 mm should not be longer than 10 feet. Hence, this requirement significantly restricts the surgeon's freedom of movement since by the time the cable is attached to the surgeon's gown, very little length remains for the surgeon to .move around the operating table.
The projection systems of conventional headlamps, both direct and compound couplings, also have disadvantages. Due to the relatively large diameter of the bundle, a directly coupled lens must have a sufficiently large aperture so as not to limit the transmitted light. Moreover, because of the size of the beam output from the cable, it is difficult to create a beam that is approximately collimated and coaxial when using a single lens system. However, when using a projection system having a compound coupling, the system then becomes quite bulky and less efficient in delivering the light from the bundle to the illumination field. The decreased efficiency results in noticeable heating of the housing of the projection system. However, the compound system tends to provide a superior quality of light, characterized as being more uniform, collimated, and coaxial. Most importantly, because of the combined inefficiencies of the above-described conventional delivery cables and projection systems, the total amount of light deliverable to the surgical field is often less than what would otherwise be desirable.
With respect to the mounting mechanisms used to support the projection systems of conventional headlamps, although many different variations exist, all of them create a bulky headband of noticeable weight. In addition, since it is a requirement that the headlamp be fixed in position after its initial adjustment, the headband itself must be secured to the surgeon's head so as to prevent any movement. Typical designs in use today consist of a circular ring adjustable in circumference to adjust the fit, with an additional support member curved over the head for supporting the delivery cable. The disadvantage of this design, aside from weight, is that it must fit rather tightly around the head to prevent any movement such that it becomes uncomfortable during lengthy surgical procedures.
Accordingly it is an object of the present invention to provide a very compact and light-weight surgical illumination system which has all the functionality of conventional illumination systems, but provides significantly improved comfort for the surgeon during its use and more versatility in the manner in which it is mounted.
It is another an object of the present invention to provide superior illumination quality of the illuminated field in both light intensity and uniformity by supplying light to a projection system through a single core fiber optic which is substantially lighter than a fiber bundle, thereby affording more freedom of movement to the surgeon while preventing fatigue.
It is yet another object of the present invention to provide a surgical illumination system having a projection system comprising a single fiber delivery light guide directly coupled to a movable field lens through use of a simple screw mechanism which is very compact and provides better illumination for smaller fields of illumination by concentrating the light beam output from the delivery fiber and conserving the total power of the transmitted light.
It is a further object of the present invention to provide a nearly collimated light beam, coaxial with the surgeon's line of sight through use of a mounting mechanism which permits the projection system to be advantageously placed between the eyes of the surgeon without hindering his sight.